Recording and reproducing sound



April 15, 1941. E. w. HULJLEGARD 2,238,734

RECORDING AND REPRODUCING SOUND- Original Filed March 17, 1938 2 Sheets-Sheet 1 APTi1 1941. E. w. HULLEGARD 2,238,734

RECORDING AND REPRODUCING SOUND Original Filed March 17, 1938 2 Sheets-Sheet 2 Enventor Eri/i l Valdemarfiu/lleyard Patented Apr. 15, 1941 U'N l-TE D STATES PATE'N T FFICE RECORDING'AND REPRODUCING SOUND Erik Waldemar: Hullegard, Stockholm, Sweden,

assignor, bymesnezassignments, .to Radio. C'orporation of America, a corporation. of Delaware Original application" March 17,, 1938; Serial N o.

Divided and this application October 17,1940, Serial No; 361,572.

In Sweden March 2' Claims. (Cl. 179"100.3)

The present inventionrelates to such systems for recording and reproducing sound through Lthe intermedium oft light-sensitive media, such as photographiclfilms and photocells, in which" the positivezandnegative half-waves of the sound oscillation curve are recorded on. the light-sensitivemediumindependent of one another tofacilitatetheir separation in the reproduction through the intermedium .of the photocells.

This .application is a division of my: application Serial No. 196,554, filed March 17, 1938.

The advantage? is afforded that no biasing illumination of lthea-light-sensitive medium is required. on'rwhichillumination the sound;oscilla'- tions are optically, superposed .so that the backgroun will be much more. silent than inlprevious syistems having a. biasing illumination. In a known. system; the, positive. and. negative halfwavesof ;the.sound curve are recordedeachcin one.

or two coextensive tracks which necessitates the provisionof.complicated apparatus having means for the simultaneous reproduction of two tracks. These two tracks require further a space of the light-sensitive medium, such as a film, which is double that of an ordinary single track.

According to the present invention, said inconvenience is eliminated by arranging that the positive and negative half-waves of the sound curve are not recorded in positions transversely displaced in relation to one another but in one and the same track while receiving such distinctive properties that the record of each halfwave could be separately reproduced. In case the film is color-sensitive, the positive and negative half-waves of the sound curve could be converted each to a light bundle of a distinctive color, to which the film is exposed.

The invention will now be more fully described with reference to the accompanying drawings illustrating, by way of example, two embodiments of the invention. On the drawings, Figure 1 is a perspective and diagrammatic view of a preferred embodiment of a recording device, whereas Figure 2 is a circuit diagram of a reproduction device, Figure 3 is a similar diagram of a recorder adapted to produce a variable density record, and Figure 4 illustrates a modified type of reproducer in which the two photoelectric elements are arranged with a single anode within the same container.

In Figure 1, condensing lenses L1 and L2 and a diagphragm S1 are positioned in a straight line between a source of light I and an oscillating mirror 2, as shown in Figure 1. The diaphragm 51 consists of an opaque or nontransparent por- F'urtl'ler:condensing lenses Lsandlu and a slitdevices: arelpositioned in a straightline between the oscillating mirrorZ and a light-sensitive-band 8 in suchan' angular relationship to the path be tween parts I and 2 that, in an average position of the .mirror 2, an image of the diaphragm Sris projectedionthe slit device S2, The sharp-edged slit '9 provided therein has a width corresponding to the-opaquezone between oppositngpoints in the diaphragm S1 so that, in. the mentioned position of the-mirror; the image :of the'opaque zone covers thexslitQ and no lightcan penetrate .to

the color-sensitive film'8.

The mirror 2 is connected to an oscillograph responsive to the sound to be recorded and which is not shown on the drawings.

When the mirror 2 starts oscillation, the image of the diaphragm S1 oscillates to and. from over the device S2 so that the translucent portions 4 and 5 alternating with the portions 6, I send light of corresponding color through the slit 9 on to the film 8. The transversal width, or, in this instance, the vertical extension of the bundle of rays reaching the film, will apparently depend on the vertical dimension of the translucent portions 4 to I projected on to the slit device and thus on the angular deflection of the mirror 2 or the amplitude of the sound wave corresponding thereto. Provided the film band 8 is moving at a sufficient rate crosswise to the slit 9, there will accordingly be recorded impressions which, when the film is developed, will appear as oblong traces l0, ll of the one or the other color on an opaque background 24, depending upon the translucent portions 4, 5 or 6, I which is operative at the moment.

sociated in push-pull connection with an fier A and a loudspeaker B.

When the colored film 8 is passed between the lenses L5 and La, the bundle of light will pass alternately traces of the one or the other color of the passing film band 8, and light of alternating color will be reflected at the mirrors I3 and M on to the filters Sc and S4 to actuate the one and the other of the photocells P1 and P2; respectively, so that the amplifier A and loudspeaker B will respond.

In the shown embodiment, there are two pairs of opposing translucent filter portions 4, 6 and 5, 1 respectively. Instead thereof, only one pair of several pairs of opposing translucent portions can be used. The points of such portions need not be positioned exactly opposite one another, reckoned in a plane parallel with the path of movement of the film band, but may be staggered, in which case the traces on the film band will be correspondingly staggered, although grouped symmetrically in regard to an imaginary base line on the film which line is parallel with the path of movement of the film.

The two photocells shown in Figure 2 could be combined, as shown in Figure 4, to a single one having, for instance, two cathodes I! and I8 and one anode [9. In this arrangement, the lenses I5 and I6 perform the same function as the reflectors l3 and M of Figure 2.

. Whereas the above-described apparatus refers to such sound films which are modulated according to the amplitude method, the invention could likewise be applied to sound films, based on an 7 intensity-modulation, and in systems using a combination of amplitudeand intensity-modulation.

Thus, if the aperture plate S1 be modified so that its center section 3 is opaque, its left-hand section 4 passes only red light, and its righthand section passes only blue light, a variable density record is produced. This'necessarily follows from the fact that, when the mirror 2 is at rest, no light is passed through the slit 9, and, when the light beam is vibrated transversely of suitable for causing light modulated by alternate half cycles to be applied respectively to the cathodes I! and I 8. The reproducer of Figure 4 is suitable'for this purpose. This reproducer is also capable of reproducing either of the two tracks of the record of Figure 1. method and apparatus are particularly useful with. the present type of color films wherein a plurality of color sensitive layers are provided and the exposure and development produce appropriate colors in each of these layers, as distinguished from earlier types of color films in which each color was printed separately on to the positive.

Having now described my invention, I claim:

1. The sound-recording method which includes recording the positive half cycles of a sound wave in the form of spaced images, each symmetrical about a common longitudinal axis of the record in one color, and recording the negative half cycles of said Wave in the form of similar spaced images, each symmetrical about the same common axis in another color.

2. The sound-recording method which includes recording the positive half cycles of a sound wave in the form of spaced images, each symmetrical about a common longitudinal axis of the record in one color, and recording the negative half cycles of said wave in the form of similar spaced images between said first images, each symmetrical about the same common axis in another color.

ERIK WALDEMAR HULLEGARD.

The foregoing. 

